1. Technical Field
The present invention relates to an ultrasound diagnostic apparatus, and more particularly to a technology of forming a three-dimensional bloodstream image.
2. Related Art
In the medical field, an ultrasound diagnostic apparatus transmits and receives ultrasonic waves to and from a living organism and generates an ultrasound image on the basis of a reception signal obtained by transmission and reception of the ultrasonic waves. Typical ultrasound images may include a two-dimensional tissue image, which is a monochrome image (B-mode image), and a two-dimensional bloodstream image, which is a color image. A two-dimensional bloodstream image is color representation of Doppler components or motion information (e.g., velocity information, power information, and so on) which are contained in a reception signal. A two-dimensional tissue image may be formed by reference to the motion information. In general, a two-dimensional tissue image and a two-dimensional bloodstream image are combined to form a combined image, which is then to be displayed on a display.
In recent years, three-dimensional ultrasound diagnostic apparatuses which form a three-dimensional tissue image by reference to volume data obtained by transmission and reception of ultrasonic waves with respect to a three-dimensional space within a living organism have been in wide-spread use. Conventionally, a three-dimensional tissue image is formed by using a volume rendering method, for example, and is a stereoscopic representation of a tissue (e.g. an organ) within a living organism. Meanwhile, motion volume data can be obtained by extracting motion information from volume data. Here, motion volume data refers to three-dimensional data formed of the motion information. By applying three-dimensional image processing to the motion volume data, a three-dimensional bloodstream image can be formed.
JP 2005-157664 A (Reference 1), JP 2005-40622 A (Reference 2), JP 2006-51202 A (Reference 3), and JP 2001-17428 A (Reference 4) disclose conventional ultrasound diagnostic apparatuses which form a three-dimensional ultrasound image.
In a case where the magnitude of velocity or power is represented by the level of brightness in forming a three-dimensional bloodstream image, provided that a bloodstream located on the front side is a low-velocity stream and a bloodstream on the further back side is a high-velocity stream, the high-velocity bloodstream located on the back side is represented with a high brightness and the low-velocity bloodstream located on the front side is represented with a low brightness, or only the high-velocity bloodstream on the back side is represented. Consequently, the resulting image loses a sense of depth, which is a characteristic of a three-dimensional image. If a weighting function is applied in the depth direction in order to prevent the above disadvantage, the magnitude of motion information such as velocity cannot be represented in an accurate manner. As such, formation of a three-dimensional bloodstream image suffers from specific problems which are inherent thereto and differ from those regarding formation of a three-dimensional tissue image.